WindowsDesktop should produce non-stable sentinel pack that is not arch-specific

[mmitche]

WindowsDesktop does not produce a package that is:

• Non arch specific
• Non-stable in stable builds.

This leads to an issue in stable VMR builds where we can't locate the windowsdesktop layout required to redist with the SDK.

Resolve. Typically it's been something like Microsoft.WindowsDesktop.Internal.